1. For the Cake: Adjust the oven rack to middle position and heat oven to 350 degrees F. Grease and flour a 13x9-inch baking pan.
2. Whisk 2 cups of flour, baking powder, and salt together in a medium bowl; set aside. With an electric mixer, beat the butter and sugars together on medium-high speed until fluffy, about 2 minutes. Add eggs, one at a time, beating until just incorporated. Reduce speed to medium and beat in one-third of the flour mixture until incorporated; beat in half of the milk. Beat in half of the remaining flour mixture, then remaining milk, and finally remaining flour mixture. Toss the blueberries with remaining 1 teaspoon flour. Using a rubber spatula, gently fold in blueberries. Spread the batter into the prepared pan.
4. For the Topping: Scatter the blueberries over top of the batter. Stir the sugar and cinnamon together in a small bowl and sprinkle evenly over the batter. Bake until toothpick inserted in center of cake comes out clean, 45 to 50 minutes. Cool in pan 20 minutes, then turn out and place on serving platter (topping side up). Serve warm or at room temperature. (Cake can be stored in an airtight container at room temperature for up to 3 days.)
* Note: If using frozen blueberries, do not let them thaw, as they will turn the batter a blue-green color.